Field
Aspects of the invention described herein relate generally to filters inserted into a patient's body and more particularly to the provision of echogenic coatings on such devices to enhance their visibility using one or more of in any combination ultrasound imaging, intravascular ultrasound imaging, greyscale intravascular ultrasound imaging, color intravascular ultrasound imaging or ultrasound image signal processing that included spectral analysis of the filter.
Background
Embolic protection is utilized throughout the vasculature to prevent the potentially fatal passage of embolic material in the bloodstream to smaller vessels where it can obstruct blood flow. The dislodgement of embolic material is often associated with procedures which open blood vessels to restore natural blood flow such as stenting, angioplasty, arthrectomy, endarterectomy or thrombectomy. Used as an adjunct to these procedures, embolic protection devices trap debris and provide a means for removal for the body.
One widely used embolic protection application is the placement of filtration means in the vena cava. Vena cava filters (VCF) prevent the passage of thrombus from the deep veins of the legs into the blood stream and ultimately to the lungs. This condition is known as deep vein thrombosis (DVT), which can cause a potentially fatal condition known as pulmonary embolism (PE).
The first surgical treatment for PE, performed by John Hunter in 1874, was femoral vein ligation. The next major advancement, introduced in the 1950's, was the practice of compartmentalizing of the vena cava using clips, suture or staples. While effective at preventing PE, these methods were associated with significant mortality and morbidity (see, e.g., Kinney T B, Update on inferior vena cava filters, JVIR 2003; 14:425-440, incorporated herein by reference).
A major improvement in PE treatment, in which venous blood flow was maintained, was presented by DeWesse in 1955. This method was called the “harp-string” filter, as represented in FIG. 1A and FIG. 1B, in which strands of silk suture 12 were sewn across the vena cava 11 in a tangential plane below the renal veins 13 to trap thrombus. Reported clinical results demonstrated the effectiveness of this method in preventing PE and maintaining caval patency. (see, e.g., DeWeese M S, A vena cava filter for the prevention of pulmonary embolism, Arch of Surg 1963; 86:852-868, incorporated herein by reference). Operative mortality associated with all of these surgical treatments remained high and therefore limited their applicability.
The current generation of inferior vena cava (IVC) filters began in 1967 with the introduction of the Mobin-Uddin umbrella 21 (FIG. 1C) which is described in further detail in U.S. Pat. No. 3,540,431. The Greenfield filter (FIG. 1D) was introduced in 1973 and is described in further detail in U.S. Pat. No. 3,952,747. These conical-shaped devices were placed endoluminaly in the IVC and utilized hooks or barbs 20, 30 to pierce the IVC wall and fix the position of the device. A variety of conical-shaped, percutaneously placed vena cava filters, based upon this concept are now available. For example, the TULIP with a filter structure 41 (FIG. 1E) further described in U.S. Pat. No. 5,133,733; the RECOVERY with a filter structure d51 (FIG. 1F) further described in U.S. Pat. No. 6,258,026; and the TRAPESE with a filter structure 61 (FIG. 1G) further described in U.S. Pat. No. 6,443,972.
The next advancement in filters added the element of recoverability. Retrievable filters were designed to allow removal from the patient subsequent to initial placement. Retrievable filters are generally effective at preventing PE yet they have a number of shortcomings, such as, for example: failure of the device to deploy into the vessel properly, migration, perforation of the vessel wall, support structure fracture, retrievability actually limited to specific circumstances, and formation of thrombosis on or about the device.
Problems associated with retrievable, conical-shaped devices, such as those illustrated in FIG. 1D, FIG. 1E and FIG. 1F, have been reported in the medical literature. These reported problems include tilting which makes it difficult to recapture the device and compromises filtration capacity. Hooks 30, 40, 50, 60 used to secure these devices have been reported to perforate the vessel wall, cause delivery complications, and fracture. A partially retrievable system is described in detail in pending U.S. Pat. No. 2004/0186512 (FIG. 1H). In this system, the filter portion 71 can be removed from the support structure 70, but the support structure remains in-vivo. All of these described devices share the common limitation that they can be retrieved from only one end. Each of the above referenced articles, patents and patent application are incorporated herein in its entirety.
Ultrasonic imaging in the medical field is widely used for a variety of applications. In addition to imaging physiological structures and tissue such as organs, tumors, vessels, and the like, it is often desirable for a physician or technician to have an image of a medical device which has been inserted into the tissue or passageway of a patient. Still further, advancements in the use of intravascular or intraluminal imaging ultrasound (positioned either within or outside of the body) before, during and after procedures has led to increasing requirements for cooperation between device and imaging modality.
A variety of approaches have been used to enhance ultrasonic imaging of devices by increasing the acoustic reflection coefficient of the devices. While echogenic materials have been described for some uses in medical devices, the conventional uses of echogenic materials has not kept pace with the advancements in applications for imaging ultrasound. Moreover, while many approaches have been attempted, there is still need for improvements that are particular to the use of specific device designs. In particular, as medical therapies and procedures continue to advance, there is, in many medical instances, a need for more specific information about a device, its placement, position, orientation or aspect in relation to another object. What is needed are further improvements to the manner and placement of echogenic enhancements to obtain these additional benefits
In view of the many shortcomings and challenges that remain in the field of endoluminal filtering, there remains a need for improved retrievable, endoluminal filters and in particular enhancements to the echogenicity of such improved filtering designs, such as those described herein.